1. Field of the Invention
This invention relates to positioning apparatus and more particularly to apparatus for positioning a plurality of carriages along a bridge which extends across a work surface.
2. Description of the Prior Art
Apparatus is necessary for accurately positioning a glass cutter in the path along which sheet glass is conveyed as it leaves a sheet glass manufacturing plant. The cooled glass continually leaving the plant must be cut both transversely and longitudinally to form sheets of predetermined sizes. The longitudinal cutting is normally performed by cutters supported from above the path of travel of the cooled sheet glass so as to cut or score the glass longitudinally as it moves through the cutting section. The irregular edges of the glass sheet must be cut as the sheet moves through the cutting section. At times a narrow defect which extends longitudinally through the glass sheet will be present. It is desirable to be able to move two adjacent cutters close together to cut out this defect. To minimize lost production it is desirable to be able to move a replacement cutter into position while the worn out cutter wheels are replaced. For these reasons positioning apparatus wherein the cutter heads are limited to movement within fixed non-overlapping zones are disadvantageous. Further as a glass sheet shifts or moves on the work surface it is often desirable to simultaneously move all cutter heads to compensate for the shifted glass sheet.
Glass cutting apparatus which provide for a bridge extending over a work surface and having positionable cutter heads attached to the bridge are well known. Such apparatus is discussed in U.S. Pat. Nos. 3,470,776 and 3,742,793. Apparatus for automatic positioning of the cutter heads is also known and is exemplified by U.S. Pat. No. 3,834,258. A disadvantage with the apparatus as shown in U.S. Pat. No. 3,834,258 is that individual cutting heads are provided to operate in individual zones and adjacent cutting heads operate only in neighboring non-overlapping zones. This presents a problem when narrow faults extend longitudinally through a glass sheet where it is desirable to have cutter heads which can be operated relatively close together in the same zone for cutting out the fault. Another disadvantage with the apparatus disclosed in U.S. Pat. No. 3,834,258 is that the cutter heads must be returned to fixed home position before being repositioned, and an entire pattern set on several cutter heads cannot be shifted without returning all the cutter heads to the home position.